Originally Posted by Bob Denman
The larger DP rigs do...
You don't realize how handy they are until you get into a tight spot at a non truck stop station and need to bring a fill hose around a pump to the passenger side fill up
The dual pump could be used if in an extreme hurry but given typically around a hundred gallons or a bit more on high speed pumps the second cap is seldom used for that
The main reason mine gets used is when traveling in winter and want to add additive I use the passenger side fill while the fuel pumps in the drivers side